Reforming process for enhanced benzene yield

ABSTRACT

A process for reforming a full boiling range naptha feed to enhance benzene yield is disclosed which first separates the feed into a C 6  fraction containing at least 10% by volume of C 7  + hydrocarbons and a C 7  + fraction, then subjecting the C 6  fraction to a catalytic aromatization process and subjecting the C 7  + fraction to a catalytic reforming process, followed by recovering the aromatics produced.

BACKGROUND OF THE INVENTION

This invention relates to a process for reforming a full-boiling rangehydrocarbon feed to enhance benzene yield by a combination of stepsincluding separating the hydrocarbon feed into fractions, thenseparately treating the fractions by catalytic reforming the recoveringthe products. More particularly, the invention relates to a process forintegrating a catalytic aromatization process which uses a catalystsuperior in reforming C₆ and C₇ paraffins with a catalytic reformingprocess utilizing a conventional reforming catalyst in a manner whichenhances the benzene yield, increases energy efficiency and efficientlyrecovers the resulting products.

In a conventional reforming process, pentanes and lighter hydrocarbons(C₅.spsb.-) are first removed with the C₆.spsb.+ stream sent to areformer followed by fractionation with the overhead sent to anextraction unit as shown in FIG. 2. While a substantial amount ofaromatics (primarily toluene, xylenes and C₉ aromatics) are producedusing a conventional reforming catalyst such as a Pt-Re gamma aluminacatalyst, this process is not designed to maximize benzene yields.

FIELD OF THE INVENTION

The reforming of petroleum hydrocarbon streams is an important petroleumrefining process which is employed to provide high octane hydrocarbonblending components for gasoline. The process is usually practiced on astraight run naphtha fraction which has been hydrodesulfurized. Straightrun naphtha is typically highly paraffinic in nature but may containsignificant amounts of naphthenes and minor amounts of aromatics orolefins. In a typical reforming process, the reactions includedehydrogenation, isomerization, and hydrocracking. The dehydrogenationreactions typically will be the dehydroisomerization ofalkylcyclopentanes to aromatics, the dehydrogenation of paraffins toolefins, the dehydrogenation of cyclohexanes to aromatics, and thedehydrocyclization of paraffins and olefins to aromatics. Thearomatization of the n-paraffins to aromatics is generally considered tobe the most important because of the high octane of the resultingaromatic product compared to the low octane ratings for n-paraffins. Theisomerization reactions include isomerization of n-paraffins toisoparaffins, the hydroisomerization of olefins to isoparaffins, and theisomerization of substituted aromatics. The hydrocracking reactionsinclude the hydrocracking of paraffins and hydrodesulfurization if anysulfur compounds remain in the feedstock. On lighter naphtha streams, itis often desirable to avoid hydrocracking because of the resulting lowcarbon number of gaseous products which are the result.

It is well known that several catalysts are capable of reformingpetroleum naphthas and hydrocarbons that boil in the gasoline boilingrange. Examples of known catalysts useful for reforming include platinumand optionally rhenium or iridium on an alumina support, platinum ontype X and Y zeolites (provided the reactants and products aresufficiently small to flow through the pores of the zeolites), platinumon intermediate pore size zeolites as described in U.S. Pat. No.4,347,394, and platinum on cation exchanged type L zeolites. U.S. Pat.No. 4,104,320 discloses the dehydrocyclization of aliphatic hydrocarbonto aromatics by contact with a catalyst comprising a type L zeolitecontaining alkali metal ions and a Group VIII metal such as platinum.

The conventional reforming catalyst is a bi-functional catalyst whichcontains a metal hydrogenation-dehydrogenation component which isusually dispersed on the surface of a porous inorganic oxide support,notably alumina. Platinum has been widely used commercially in recentyears in the production of reforming catalysts, and platinum on aluminacatalyst have been commercially employed in refineries for the past fewdecades. In the last decade, additional metallic components have beenadded to platinum as promoters to further the activity or selectivity,or both, of the basic platinum catalyst, e.g., iridium, rhenium, tin andthe like. Some catalysts possess superior activity, or selectivity, orboth, as contrasted with other catalysts. Platinum-rhenium catalysts, byway of example, possess high selectivity in contrast to platinumcatalysts. Selectivity is generally defined as ability of the catalystto produce yields of C₅.spsb.+ liquid products with concurrent lowproduction of normally gaseous hydrocarbons, i.e., methane and propane.

There exist several processes for dividing naphtha feedstock into ahigher boiling and a lower boiling cut and reforming these cutsseparately. U.S. Pat. No. 2,867,576 discloses separating straight runnaphtha into lower and higher boiling cuts, in which the higher boilingcuts are reformed with a hydrogenation-dehydrogenation catalyst with theliquid reformate produced being passed to an aromatics separationprocess. The paraffinic fraction obtained from the separation process isblended with the lower boiling naphtha fraction and the resulting blendis reformed with a reforming catalyst which may or may not be the sametype employed in reforming the high boiling cut.

U.S. Pat. No. 2,944,959 discloses fractionating a full straight rungasoline into a light paraffinic fraction (C₅ and C₆) which ishydroisomerized with hydrogen and a pt-alumina catalyst, a middlefraction (end point of 320° to 360° F.) which is catalytically reformedwith hydrogen and a pt-alumina catalyst, and a heavy fraction which iscatalytically reformed with a molybdinum oxide catalyst and recoveringthe liquid products. U.S. Pat. Nos. 3,003,949, 3,018,244 and 3,776,949also disclose fractionating a feed into a C₅ and C₆ fraction which isisomerized and a heavier fraction which is reformed.

Other processes for dividing feedstocks and separately treating theminclude: U.S. Pat. Nos. 3,172,841 and 3,409,540 which discloseseparating fractions of a hydrocarbon feed and catalyticallyhydrocracking and catalytically reforming various fractions of the feed;U.S. Pat. No. 4,167,472 which discloses separating straight chain fromnon-straight chain C₆ -C₁₀ hydrocarbons and separately converting toaromatics; and U.S. Pat. No. 4,358,364 which discloses catalyticallyreforming a C₆ to 300° F. B.P. fraction and producing additional benzeneby hydrogasifying a C₅.spsb.- fraction, a fraction with a B.P. above300° F. and the gas stream produced from the catalytic reforming.

U.S. Pat. No. 3,753,891 discloses fractionating a straight run napthainto a light naphtha fraction containing the C₆ and a substantialportion of the C₇ hydrocarbons and a heavy naptha fraction boiling fromabout 200° to 400° F.; then reforming the light fraction to convertnaphthenes to aromatics over a pt-alumina catalyst or a bimetallicreforming catalyst; separately reforming the heavy fraction; thenupgrading the reformer effluent of the low boiling fraction over a ZSM-5type zeolite catalyst to crack the paraffins; and recovering an effluentwith improved octane rating.

While these patents disclose split feed reforming, these patents do notdisclose enhancing benzene yield by: splitting a feed into a C₆ fractioncontaining at least 10% by volume of C₇.spsb.+ hydrocarbons and aC₇.spsb.+ fraction; catalytically aromatizing the C₆ fraction over acatalyst superior in reforming C₆ and C₇ paraffins; catalyticallyreforming the C₇.spsb.+ fraction; and recovering the effluents.

SUMMARY OF THE INVENTION

It has now been found that the benzene yields produced upon reforming afull boiling range hydrocarbon feed can be increased with improvedefficiencies by first separating the feed into three fractions, aC₅.spsb.- fraction, a C₆ fraction containing at least 10% by volume ofC₇.spsb.+ hydrocarbons, and a C₇.spsb.+ fraction. The C₆ fraction issubjected to a catalytic aromatization process and a C₅.spsb.+ effluentis separated. The C₇.spsb.+ fraction is subject to a catalytic reformingprocess and a C₈.spsb.- effluent is separated from a C₉.spsb.+ effluent.The C₅.spsb.+ effluent from the catalytic aromatization unit and theC₈.spsb.- effluent from the catalytic reformer are then mixed and thearomatic content is recovered. This process maximizes the benzeneproduction by efficiently producing benzene from a C₆ fraction bycatalytic aromatization and also obtains the benefits of benzeneproduction of the C₇.spsb.+ fraction in a catalytic reformer.

DESCRIPTION OF THE DRAWINGS

The reforming processes will be described in more detail by reference tothe drawings of which:

FIG. 1 is a flow diagram of the reforming process of the invention.

FIG. 2 is a flow diagram of a conventional reforming process.

DETAILED DESCRIPTION OF THE INVENTION

In accord with this invention, the first step of this process involvesseparating a full boiling range hydrocarbon feed into three fractions(cuts). The three fractions are a C₅.spsb.- fraction (hydrocarbonshaving a five carbon atom content or less), a C₆ fraction containing atleast 10% by volume of C₇.spsb.+ hydrocarbons and a C₇.spsb.+ fraction(hydrocarbons containing seven carbon atoms and greater). Thisseparation is suitably and preferably carried out in distillationcolumns to give the specified fractions. Unless otherwise specified, thefractions contain greater than 90%, preferably at least 95% of thestated hydrocarbons. Advantageously, the C₆ fraction containing at least10 vol.% of C₇.spsb.+ hydrocarbons can be separated in a fractionatorwith less energy being required as compared to having a C₆ fraction witha lower C₇.spsb.+ content. For example, fractionating a C₆ fractioncontaining 15% C₇.spsb.+ hydrocarbons requires 15% less energy thatfractionating a C₆ fraction containing 5% C₇.spsb.+ hydrocarbons.Generally, the C₆ fraction contains from 10 to 50% by volume ofC₇.spsb.+ hydrocarbons, and preferably from 15 to 35% by volume ofC₇.spsb.+ hydrocarbons. The fractionation can be carried out, as shownin FIG. 1, wherein the hydrocarbon feed is first fractionated into theC₅.spsb.- fraction and a C₆.spsb.+ fraction in the first column and thenin a second column separated into the C₆ fraction and the C₇.spsb.+fraction.

The separated C₆ fraction which contains at least 10% by volume ofC₇.spsb.+ hydrocarbons, is then subject to a catalytic aromatizationprocess wherein it is contacted with a catalyst which at elevatedtemperatures and in the presence of hydrogen causes the C₆ and greaterparaffins to form into six carbon atom rings and thereafter causes theserings to dehydrogenate to aromatics. The aromatization catalyst for thisprocess include catalysts which convert the C₆ paraffins to benzene at ahigh selectivity and yield generally converting C₆ paraffins at a yieldof at least 30% by volume of C₆ paraffins in the feed and a selectivityof at least 50% of the C₆ paraffins to benzene, preferably converting C₆paraffins to benzene at a yield of at least 40% by volume of C₆paraffins in the feed and at a selectivity of at least 55% of C₆paraffins to benzene. Suitable catalysts include non-acidic catalystswhich contain a non-acidic carrier and at least one noble metal of GroupVIII of the periodic table. In general the catalyst employed willcomprise other elements including those from Groups 6-B, 7-B, 1-B, 4-A,6-A of the periodic table, loaded on an amorphous silica, amorphousalumina or zeolitic supports with the preferred catalysts being chosenfor its ability to maximize benzene yield.

The preferred catalyst is a platinum-zeolite L (see U.S. Pat. No.4,104,320 which is incorporated herein by reference). This catalyst hasbeen shown to have high yields and selectivity in producing aromaticcompounds from paraffins, more specifically providing efficientdehydrocyclization of C₆ paraffins. The Zeolite L and its preparation isdescribed in U.S. Pat. Nos. 3,216,789 and 3,867,512 and in U.K.Application No. 82-14147, filed May 14, 1982. The aromatization iscarried out with a catalyst comprising a Type L Zeolite having anexchangeable cations and a noble metal having a dehydrogenating effect.Generally at least 90% of the exchangeable cations are metal ionsselected from sodium, lithium, barium, calcium, potassium, strontium,rhubidium and cesium with the preferred metal ion being potassium. TheZeolite L also contains at least one metal selected from the groupconsisting of metals of Group VIII of the periodic table of elements,tin and germanium, said metal or metals including at least one metalfrom Group VIII of the periodic table having a dehydrogenating effectwith the preferred noble metal being platinum, preferably at a range of0.1-1.5% by weight. With a pt-K Zeolite L catalyst yields of 40 to 50%by volume of C₆ paraffins in the feed and a selectivity of 55 to 70% ofthe C₆ paraffins to benzene have been observed. The dehydrocyclizationis carried out in the presence of hydrogen, generally at hydrogen tohydrocarbon mole ratios of 2 to 20, preferably 3 to 10, pressures offrom about 110 to 1750 KPa and at temperatures of about 430° to 550° C.

The effluent from the catalytic aromatization of the C₆ fractioncontains a high yield of benzene from which a C₅.spsb.+ effluent isseparated. In addition, the C₇.spsb.+ hydrocarbons in the C₆ fractionare efficiently converted to aromatics such as toluene. A C₅.spsb.+effluent is efficiently separated from the effluent of the aromatizationunit due to the level of C₇.spsb.+ hydrocarbons present in the effluent.The C₇.spsb.+ hydrocarbons present in the C₅.spsb.+ effluent act as aheavy oil wash in the flash drum to efficiently remove the C₅.spsb.+hydrocarbons from the effluent.

Recovery of C₅.spsb.+ hydrocarbons, especially benzene from a streamcontaining a high benzene yield, (i.e. greater than 30 vol.%) usingconventional techniques, is difficult. For example, in a reformingprocess containing 50 vol.% benzene (<1% C₇.spsb.+ hydrocarbons),conventional recovery techniques utilizing a flash drum result in therecovery of only about 80% by volume of the benzene in the effluent. Inthis process, with the presence of at least 10% C₇.spsb.+ hydrocarbonsin the C₆ fraction and the resultant C₇.spsb.+ hydrocarbons in theeffluent, the recovery of C₅.spsb.+ hydrocarbons, especially benzene isdramatically improved. For example where the effluent contains 50 volume% benzene and 25 volume % C₇.spsb.+ hydrocarbons about 90% by volume ofthe benzene in the effluent is recovered in a flash drum.

The separated C₇.spsb.+ fraction is subjected to catalytic reformingwith a conventional reforming catalyst. That is, it is contacted with acatalyst which at elevated temperatures and in the presence of hydrogencauses the dehydrogenation of the C₇.spsb.+ alkylcyclohexanes toalkylaromatics, the dehydroisomerization of alkylcyclopentanes toalkylaromatics, the dehydrocyclization of C₇.spsb.+ paraffins toalkylaromatics and the isomerization of normal paraffins toiso-paraffins. Suitable catalysts for this purpose are acidic noblemetal catalysts such as platinum on an acidic alumina carrier. Suchcatalysts may contain more than one noble metal and additionally maycontain other metals, preferably transition metals such as rhenium,iridium, tungsten, tin, bismuth and the like and halogens such aschlorine or fluorine. Catalysts of this type are available commercially.A preferred reforming catalyst is a platinum-rhenium on gamma aluminacatalyst. The conventional reforming catalysts are generally efficientin converting C₇.spsb.+ hydrocarbons but are generally not as effectivein producing benzene from C₆ paraffins as the aromatization catalyst. Ingeneral, the reforming catalysts convert C₆ paraffins at a yield of lessthan 30% by volume of C₆ paraffins in the feed and a selectivity of lessthan 35% of C₆ paraffins to benzene.

The catalytic reforming of the C₇.spsb.+ fraction is suitably carriedout at temperatures of from about 400°-600° C., preferably at atemperature at least sufficient to convert at least 90% of the C₉paraffins. For a platinum-rhenium gamma alumina catalyst, a temperaturesufficient to convert the C₉ paraffins is generally at least 480° C.Conversion of the C₉ paraffins is desired in order to eliminate enoughof the C₉ paraffins from the reformer effluent to produce in the solventextraction process an aromatic extract containing a low level ofnon-aromatics. Since the C₉ paraffins boil in the same range as the C₈aromatics they are difficult to remove by fractionation and in a solventextraction process, solvents such as sulfolane do a poor job inseparating C₉ paraffins from the aromatics. Thus, an effective way ofobtaining an aromatic extract from the solvent extraction unit with alow or on-specification level of non-aromatics, such as C₉ paraffins, isto insure the C₉ paraffins are converted during catalytic reforming. Thecatalytic reforming is generally carried out with pressures of fromabout 700 to 2750 KPa and at weight hourly space velocities of 0.5 to 10and hydrogen to feed molar ratios from about 2 to 15.

The effluent from the catalyst reforming of the C₇.spsb.+ fraction isthen separated into a C₈.spsb.- effluent and a C₉.spsb.+ effluent. Thenthe C₅.spsb.+ effluent from the catalytic dehydrocyclization unit andthe C₈.spsb.- effluent from the catalytic reforming unit are mixed andan aromatic extract and non-aromatic raffinate are recovered. Theresultant aromatic extract contains a high yield of benzene which hasbeen produced in an energy efficient manner. The benzene yield thusachieved for the process of this invention is in the range of 5 to 25%by volume of the C₆.spsb.+ hydrocarbons and 35 to 80% by volume of theC₆ hydrocarbons in the full boiling range hydrocarbon feed, whichcompares to a benzene yield in a conventional reforming process as shownin FIG. 2, of about 2 to 10% by volume of C₆.spsb.+ hydrocarbons and 10to 35% by volume of the C₆ hydrocarbons in the full boiling rangehydrocarbon feed. In general, for the same hydrocarbon feed, with theprocess of this invention there will be an increase of the benzene yieldof about 1.5 to 3 times the benzene yield of a conventional reformingprocess as shown in FIG. 2.

The aromatic extract and non-aromatic raffinate are efficientlyrecovered in an aromatics recovery unit, i.e. a solvent extractionprocess which uses a solvent selective for aromatics such as sulfolaneor tetraethylene glycol. The C₈.spsb.- effluent is preferably furtherseparated into a C₆.spsb.- effluent, a C₇ effluent and a C₈ effluent,with the C₆.spsb.- and C₈ effluents being mixed with a C₅.spsb.+effluent from the catalytic aromatization unit for subsequent recoveryof an aromatics extract in the solvent extraction unit. In this way theeffluent containing the C₇ hydrocarbons (mostly toluene) and theeffluent containing C₉.spsb.+ hydrocarbons are not processed in thesolvent extraction process which increases the efficient use of thesolvent extraction process to recover the more valuable aromatics ofbenzene, xylenes and ethylbenzene. The separation of the effluent fromthe catalytic reforming unit can be efficiently carried out by firstfractionating the effluent, as shown in FIG. 1, into a C₆.spsb.-effluent, a C₇ effluent and a C₈.spsb.+ effluent, then fractionating theC₈.spsb.+ effluent into a C₈ effluent and a C₉.spsb.+ effluent.

The non-aromatic raffinate recovered from the solvent extraction processmay be recycled and added to the C₆ fraction feed for catalyticdehydrocyclization which increases the benzene yield of the process.

EXAMPLE 1

This example shall be described with reference to the flow diagram ofFIG. 1 and the various hydrocarbon streams and units identified therein.A full boiling range naptha feedstream, comprising a range ofhydrocarbons from C₃ to those boiling up to about 350° F. and containing51.2% paraffins, 36% naphthenes and 12.8% aromatics is fed intodistillation tower 1 to separate a C₅.spsb.- fraction from a C₆.spsb.+fraction. The resultant C₆.spsb.+ fraction contains 0.7% of C₅hydrocarbons, 5.4% C₁₀.spsb.+ hydrocarbons, 17.9% C₆ hydrocarbons and76% C₇ to C₉ hydrocarbons while the C₅.spsb.- fraction contains 6% C₆hydrocarbons and the remainder C₅.spsb.- hydrocarbons (all % by volume).The tower 1 utilizes 0.15 MBTU per barrel of feed.

The C₆.spsb.+ fraction from distillation tower 1 is then fed intodistillation tower 2 to separate a C₆ fraction which contains at least10% C₇.spsb.+ hydrocarbons from a C₇.spsb.30 fraction. The resultant C₆fraction contains 3.2% C₅ hydrocarbons, 72.7% C₆ hydrocarbons and 24.1%C₇.spsb.+ hydrocarbons, with the C₇.spsb.+ fraction containing 1.5% C₆hydrocarbons, 91.9% C₇ to C₉ hydrocarbons and 6.6% C₁₀.spsb.+hydrocarbons (all % by volume). The tower 2 energy usage was 0.36MBTU/barrel of feed. To decrease the C₇.spsb.+ content in the C₆fraction to 5% would require an energy usage of 0.46 MBTU/barrel offeed.

The C₆ fraction is fed into the aromatizer reactor 3 which contains a KZeolite L catalyst containing 0.6% by weight of platinum with thedehydrocyclization reaction taking place at a temperature of 510° C., aweight hourly space velocity of 2.5, a pressure of 860 KPa and ahydrogen to hydrocarbon mole ratio of 6. The effluent from thearomatizer reactor 3 contains 32% benzene, 12%, toluene (all % byvolume). The effluent is then fed into a flash drum 4 to separate aC₅.spsb.+ effluent with about 90% of the benzene being recovered in theflash drum. The C₄.spsb.- stream containing hydrogen from the flash drum4 is then recycled as needed to the aromatizer reactor 3 with excessused as make gas. The C₅.spsb.+ effluent is then fed into a stabilizer 5to further purify and remove any C₄.spsb.- hydrocarbons.

The C₇.spsb.+ fraction is fed into a conventional reformer 6 whichcontains a pt-Re gamma-alumina catalyst with the reforming reactiontaking place at temperatures of 919° F. (493° C.), a weight hourly spacevelocity of 1.3, a pressure of 1413 KPa, a recycle gas rate of 2.3KSCF/Bbl with the unit operated to give an octane of 103. The reformereffluent contains C₅.spsb.- hydrocarbons, 1.8% benzene, 3.2% other C₆hydrocarbons (excluding benzene), 12.3% toluene, 25.1% xylenes and 24%C₉.spsb.+ hydrocarbons (all % by volume of reformer feed). The reformereffluent is then fed into a toluene rejection tower 7 from which a C₇effluent containing 92% C₇ hydrocarbon (mostly toluene) is taken as asidestream, a C₆.spsb.- effluent containing 14.1% C₅.spsb.-hydrocarbons, 11.8% benzene, 22.3% other C₆ hydrocarbons (excludingbenzene) and 51.8% C₇ hydrocarbons is taken overhead and a C₈.spsb.+effluent containing 3.6% C₇, 49.5% C₈ hydrocarbons (mostly xylenes) and46.9% C₉.spsb.+ hydrocarbons (mostly aromatics) is taken from the bottom(all % by volume). The C₈.spsb.30 effluent is then further distilled ina C₈ /C₉ splitter tower 8 from which a C₈ effluent containing 96% C₈hydrocarbons and 4% C₉.spsb.+ and a C₉.spsb.+ effluent containing 1% C₈hydrocarbons and 99% C₉.spsb.+ hydrocarbons is recovered.

The C₅.spsb.+ effluent from the aromatizer and the C₆.spsb.- effluentand C₈ effluent from the reformer are then mixed and fed into theextraction unit 9 which utilizes sulfolane to solvent extract aromaticswith the aromatics extract stream containing 30% benzene, 18% tolueneand 51.8% C₈ aromatics while the non-aromatic raffinate stream contains0.2% aromatics. The non-aromatic raffinate stream is then advantageouslyfeed back to tower 2 to produce benzene. The resultant benzene yield is12.9% by volume of the C₆.spsb.+ hydrocarbons in the feedstream and 66%by volume of the C₆ hydrocarbons in the full boiling range napthafeedstream.

EXAMPLE 2

This comparative example shall be described with reference to the flowdiagram of FIG. 2. The full boiling range naptha feedstream of Example 1is fed into distillation tower 10 to produce a C₆.spsb.+ fraction as inExample 1.

The C₆.spsb.+ fraction is fed into conventional reformer 11 whichcontains a Pt-Re gamma-alumina catalyst with the reforming reactionoperated at a temperature of 920° F. (493° C.), a weight hourly spacevelocity of 1.3, a pressure of 1400 KPa, a recycle gas rate of 2.3KSCF/B with the unit operated to give an octane of 101. The resultanteffluent contains 4% benzene, 11% other C₆ hydrocarbons, 11.6% toluene,4.5% other C₇ hydrocarbons, 20% C₈ aromatics, 19% C₉.spsb.+ hydrocarbonsand balance being C₅.spsb.- hydrocarbons (all % by volume of feed).

The reformer effluent is fed into a C₈ /C₉ splitter tower 12 to separatethe C₈.spsb.- effluent from the C₉.spsb.+ effluent. The C₈.spsb.-effluent contains 2% C₅ hydrocarbons, 28.6% C₆ hydrocarbons, 66.2% C₇hydrocarbons and 3.2% C₉.spsb.+ hydrocarbons and the C₉.spsb.+ effluentcontains 1% C₈ and the balance C₉.spsb.+ hydrocarbons.

The C₈.spsb.- effluent is fed to a sulfolane extraction unit 13 fromwhich an aromatic extract containing 12.8% benzene, 31.3% toluene, 53.4%C₈ aromatics, 2.3% C₉.spsb.+ aromatics and the balance C₉.spsb.+non-aromatics hydrocarbons. The resultant benzene yield is 5.2% byvolume of the C₆.spsb.30 hydrocarbons in the feedstream and 27.5% byvolume of the C₆ hydrocarbons in the full boiling range napthafeedstream.

What is claimed is:
 1. A process for reforming a full boiling range hydrocarbon feed to enhance benzene yield comprising:(a) separating the hydrocarbon feed into a C₅.spsb.- fraction, a C₆ -C₇ fraction containing at least 10% by volume of C₇.spsb.+ hydrocarbons, and a C₇.spsb.+ fraction; (b) subjecting the C₆ -C₇ fraction to catalytic aromatization at elevated temperatures in the presence of hydrogen and utilizing a catalyst containing a non-acidic carrier and at least one Group VIII noble metal which catalyst converts C₆ paraffins to benzene in a yield of at least 30% by volume and a selectivity of at least 50% and separating a C₅.spsb.+ effluent; (c) subjecting the C₇.spsb.+ fraction to catalytic reforming at elevated temperatures in the presence of hydrogen utilizing a catalyst comprising platinum on an acidic alumina carrier and separating a C₈.spsb.- effluent from a C₉.spsb.+ effluent; (d) mixing the C₅.spsb.+ effluent and C₈.spsb.- effluent from steps (b) and (c) and recovering an aromatic extract and a non-aromatic raffinate.
 2. Process of claim 1 wherein the C₅.spsb.+ effluent is separated in a flash drum.
 3. Process of claim 2 wherein the C₆ fraction contains 15 to 35% by volume of C₇.spsb.+ hydrocarbons.
 4. Process of claim 1 wherein the catalyst for catalytic aromatization converts C₆ paraffins into benzene at a selectivity of at least 50% of the C₆ paraffins to benzene and the catalyst for catalytic reforming converts C₆ paraffins into benzene at a selectivity of less than 35% of C₆ paraffins to benzene.
 5. Process of claim 4 wherein the aromatic extract and non-aromatic raffinate are recovered in a solvent extraction process.
 6. Process of claim 5 wherein the catalytic reforming is carried out at temperatures sufficient to convert at least 90% of the C₉ paraffins.
 7. Process of claim 6 wherein the catalytic reforming is carried out with a platinum-rhenium gamma alumina catalyst at temperatures of from about 480° C. to 510° C.
 8. Process of claim 6 wherein the non-aromatic raffinate recovered in the solvent extraction process is recycled and added to the full boiling range naphtha prior to the separation of step (a).
 9. Process of claim 5 further comprising separating the C₈.spsb.- effluent into a C₆.spsb.- effluent, a C₇ effluent and a C₈ effluent and only the C₆.spsb.- effluent and the C₈ effluent are mixed with the C₅.spsb.+ effluent for the recovery of the aromatic extract in the solvent extraction process.
 10. Process of claim 9 wherein the effluent from the catalytic reforming are separated by first fractionating the effluent into a C₆.spsb.- effluent, a C₇ effluent and a C₈.spsb.+ effluent, then fractionating the C₈.spsb.+ effluent into a C₈ effluent and a C₉.spsb.+ effluent.
 11. Process of claim 5 wherein the non-aromatic raffinate recovered in the solvent extraction process is recycled and added to the C₆ fraction in step (b) for catalytic aromatization.
 12. Process of claim 5 wherein the solvent extraction process uses a solvent selected from the group consisting of sulfolane and tetra ethylene glycol.
 13. Process of claim 4 wherein the C₆ fraction contains 10 to 50% by volume of C₇.spsb.+ hydrocarbons.
 14. Process of claim 1 wherein the platinum on acidic alumina catalyst also contains a metal chosen from the group consisting of rhenium, iridium, tungsten, tin and bismuth.
 15. Process of claim 1 wherein the catalyst for catalytic aromatization converts the C₆ paraffins into benzene at a yield of at least 40% by volume of C₆ paraffins in the feed and at a selectivity of at least 55% of C₆ paraffins to benzene.
 16. Process of claim 15 wherein the catalyst for catalytic aromatization is a platinum type L zeolite catalyt wherein at least 90% of the exchangeable cations are metal ions selected for sodium, lithium, barium, calcium, potassium, strontium, rubidium and cesium.
 17. Process of claim 16 wherein the benzene yield is from 5 to 25% by volume of the C₆.spsb.+ hydrocarbons and 35 to 80% by volume of the C₆ hydrocarbons in the full boiling range hydrocarbon feed.
 18. The process of claim 15 where the catalyst is platinum potassium type L zeolite.
 19. Process of claim 1 wherein the hydrocarbon feed is a naphtha having a boiling range up to about 350° F. 